Author(s): Lindy Liu, Jay Gee, David Blaney

Infectious Agent

Burkholderia pseudomallei, a saprophytic gram-negative bacillus, is the causative agent of melioidosis. The bacteria are found in soil and water and are widely distributed in tropical and subtropical countries.

Transmission

B. pseudomallei can infect both animals and humans through damaged skin (e.g., open wounds, cuts, burns) or mucous membranes. Damaged skin coming in direct contact with contaminated soil or water is the most frequent route for natural infection. Ingestion and inhalation are two other routes of infection. The risk of spread from person-to-person is considered extremely low as there are few documented cases of transmission via this route.

Epidemiology

Melioidosis goes underreported or unrecognized in many tropical and subtropical areas; >165,000 cases are estimated to occur annually, mainly in Southeast Asia and in northern Australia. B. pseudomallei is endemic to Southeast Asia, Papua New Guinea, much of the Indian subcontinent, southern China, Hong Kong, and Taiwan. It is considered highly endemic to northeast Thailand, Malaysia, Singapore, and northern Australia.

B. pseudomallei has also been found in the Americas, including the Caribbean and the Gulf Coast of the United States (Mississippi). Sporadic cases of disease have been reported among residents of or travelers to Aruba, British Virgin Islands, Colombia, Costa Rica, Ecuador, El Salvador, Guatemala, Guadeloupe, Guyana, Honduras, Martinique, Mexico, Panama, Peru, Puerto Rico, US Virgin Islands, and Venezuela. Clusters of melioidosis have been reported in northeastern Brazil. The true extent of distribution the bacteria remains unknown.

Among the average of 12 melioidosis cases reported annually to the Centers for Disease Control and Prevention (CDC), most occur in people with a history of recent travel to a region where B. pseudomallei is known to be endemic. Risk for infection is greatest for adventure travelers, construction and resource extraction workers, ecotourists, military personnel, and other people whose contact with contaminated soil or water might expose them to the bacteria. The bacteria can also be present in untreated water and raw or undercooked food. Infections have been reported in people who spent <1 week in an endemic area. Cases, especially those presenting as pneumonia, are often associated with periods of high rainfall (e.g., during typhoons or the monsoon season).

Even in regions where melioidosis is highly endemic (e.g., northern Australia, Thailand), most healthy people exposed to B. pseudomallei never develop melioidosis. People with certain conditions, however, are at greater risk for disease. Risk factors for developing melioidosis include diabetes, excessive alcohol use, chronic lung disease (e.g., chronic obstructive pulmonary disease or cystic fibrosis), chronic renal disease, thalassemia, and malignancy or other non-HIV–related immune suppression.

Clinical Presentation

Incubation period is generally 1–21 days, with a median of 4 days; people who receive a high inoculum can become symptomatic within a few hours. Melioidosis also can remain latent for months or years before symptoms develop. It can present as a localized infection, pneumonia, bacteremia, or disseminated infection involving any organ, including the brain.

Symptoms are nonspecific and will vary depending on the route of infection. Symptoms can include abdominal discomfort; abscesses or ulcerations; chest pain, cough, and respiratory distress; disorientation, headache, and seizures; fever; localized pain and swelling; muscle or joint pain; and weight loss. Patients generally present with acute illness, but ≈9% present with ≥2 months of symptoms. Chronic melioidosis often mimics Mycobacterium tuberculosis infection clinically. Subclinical infection is also possible.

Diagnosis

Prompt diagnosis and treatment are critical. Guided by clinical syndrome, collect specimens from all relevant infection sites for culture. Depending on the site(s) of suspected infection, recommended specimens for collection include blood, cerebrospinal fluid, pericardial fluid, peritoneal fluid, purulent exudate (from skin or internal abscesses), sputum, synovial fluid, and urine; throat and rectal swabs can also be collected. Culturing B. pseudomallei from any clinical specimen is diagnostic for melioidosis because the bacterium is not considered part of the natural microbiota. Alert clinical laboratory personnel in advance that specimen cultures may grow B. pseudomallei and to follow proper safety precautions.

Although an indirect hemagglutination assay (IHA) is widely used, no serologic test can confirm melioidosis. In the United States, the Laboratory Response Network can perform confirmatory testing on isolates. CDC laboratories can conduct confirmatory testing in addition to other complex tests (e.g., antimicrobial susceptibility testing, IHA, and genetic analysis by whole-genome sequencing). Submissions to CDC are handled through coordination with local or state public health labs; clinicians should consult local or state public health departments to arrange testing.  See information and procedures for submitting specimens to CDC’s Bacterial Special Pathogens Branch in the Division of High-Consequence Pathogens and Pathology.

Treatment

Treatment of melioidosis requires long-term antibiotic therapy (acute phase followed by eradication phase), and consultation with an infectious disease or tropical medicine specialist is strongly advised. Intravenous ceftazidime, or meropenem for severe cases with sepsis, is typically used for initial treatment, for a minimum of 14 days. Depending on response to therapy, clinicians can extend intravenous treatment for up to 8 weeks in severe cases. After initial treatment, provide 3–6 months of eradication treatment with oral trimethoprim-sulfamethoxazole (TMP-SMX) or amoxicillin-clavulanic acid (for patients unable to tolerate TMP-SMX). Relapses can occur, especially in patients who receive a shorter-than-recommended course of therapy.

Prevention

People who live in or who visit areas where B. pseudomallei is endemic—especially those individuals with underlying health conditions that place them at increased risk for developing melioidosis—should follow the precautions listed in Box 5-01.

CDC website: Melioidosis